26-12-2020, 02:00 PM
pictures below is of the latest prototype.
The prototype board is just used as a temporary bracket to hold the display in a position that it can be seen. Otherwise the display just flaps about and usually ends up face down.
It looks similar to the last one but they are quite a number of circuit changes.
The microcontroller is changed from a 18LF26K22 to a 18F26K22 and is now operating with 5V logic levels.
I was using the 18LF26k22 with 3.3V logic levels to match in with the 3.3V logic levels of the FPGA.
But the LCD display I decided to use is a 5V type and it didn't take kindly to the 3.3V logic levels from the 18LF26K22 resulting with some corrupted charters on the display.
Display NHD-02161Z-FSY-YBW-C
Writing twice to the display gave satisfactory results but I didn't think it good enough to leave it like that so I decided to change the microcontroller to 5V logic.
As communication is only one way between the microcontroller and the FPGA it was easy to drop the logic levels from 5V to 3.3V using potential dividers to suit the FPGA.
Because the audio gets fed to both modulator chips dependant on what standard is selected another Audio Gain pot would be needed for the second modulator.
Instead of using a second pot I have removed the one that was there and replaced it with a Digipot. With the Digipot a different level can be set for each preset if needed.
Digipot MCP40D18T-503E/LT
I am also trialling a DC to DC converter instead of the LM7805 if it don't cause any problems it will be a keeper as it has dramatically reduced heat dissipation.
It has the same footprint as the LM7805 so is easily converted if any issues arise.
DC to DC converter OKI-78SR-5/1.5-W36-C
Frank
The prototype board is just used as a temporary bracket to hold the display in a position that it can be seen. Otherwise the display just flaps about and usually ends up face down.
It looks similar to the last one but they are quite a number of circuit changes.
The microcontroller is changed from a 18LF26K22 to a 18F26K22 and is now operating with 5V logic levels.
I was using the 18LF26k22 with 3.3V logic levels to match in with the 3.3V logic levels of the FPGA.
But the LCD display I decided to use is a 5V type and it didn't take kindly to the 3.3V logic levels from the 18LF26K22 resulting with some corrupted charters on the display.
Display NHD-02161Z-FSY-YBW-C
Writing twice to the display gave satisfactory results but I didn't think it good enough to leave it like that so I decided to change the microcontroller to 5V logic.
As communication is only one way between the microcontroller and the FPGA it was easy to drop the logic levels from 5V to 3.3V using potential dividers to suit the FPGA.
Because the audio gets fed to both modulator chips dependant on what standard is selected another Audio Gain pot would be needed for the second modulator.
Instead of using a second pot I have removed the one that was there and replaced it with a Digipot. With the Digipot a different level can be set for each preset if needed.
Digipot MCP40D18T-503E/LT
I am also trialling a DC to DC converter instead of the LM7805 if it don't cause any problems it will be a keeper as it has dramatically reduced heat dissipation.
It has the same footprint as the LM7805 so is easily converted if any issues arise.
DC to DC converter OKI-78SR-5/1.5-W36-C
Frank
